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Voltage measurement apparatus and electrically-driven toolVoltage measurement apparatus and electrically-driven tool description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070029967, Voltage measurement apparatus and electrically-driven tool. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a voltage measurement apparatus which measures the voltage of a battery-cell group that is made up of a plurality of battery cells connected in series. [0003] 2. Description of the Background Art [0004] In recent years, in an electric car, a hybrid car, an electrically-driven tool or the like, an electrically-driven motor has been widely used as a mechanical power source or an auxiliary mechanical power source. As a power supply source to an electrically-driven motor, a battery-cell group formed by a secondary battery has been popular which is made up of a plurality of battery cells connected in series. For example, as such a battery-cell group, there is a 1.2-volt nickel-hydrogen battery, and a battery-cell group formed by connecting 240 cells in series is well known. In this battery-cell group, each battery cell has various temperature characteristics or capacitances. Hence, in the process of a charge or a discharge, an overcharge or an over-discharge may be generated in some cells. In order to prevent such an overcharge or over-discharge, it is essential to measure not only the voltage of a battery-cell group as a whole, but also the voltage of individual battery cells or each battery-cell block made up of a predetermined number of cells. [0005] As a prior art of measuring the voltage of each battery cell which makes up a battery-cell group, for example, a flying capacitor circuit is known which is described in Japanese Patent Laid-Open No. 2001-201522 specification. FIG. 9 is a circuit diagram, showing the configuration of the flying capacitor circuit according to the prior art. As shown in FIG. 9, this flying capacitor circuit includes: a battery-cell group 100 which is formed by connecting N battery cells in series; cell-selection switch groups 200, 300 which choose any battery cell from the battery-cell group 100; a sampling switch 400; a transfer switch 600; an A/D converter 700. [0006] A basic operation of the flying capacitor circuit will be described using FIG. 9. Specifically, the cell-selection switch groups 200, 300 choose any battery cell included in the battery-cell group 100. Then, the sampling switch 400 operates so that a capacitor 500 is charged by the chosen battery cell. After it has been charged, the sampling switch 400 is turned off and the transfer switch 600 is turned on. Thereby, the voltage of the charged capacitor 500 is transformed into a digital value by the A/D converter 700. Consequently, the chosen cell's voltage can be obtained by the sampling switch 400. [0007] Herein, an electric switch is each used as the above described cell-selection switch groups 200, 300, sampling switch 400 and transfer switch 600. This electric switch is sure to have a parasitic capacitance. Hence, when the capacitor 500 is charged by any battery cell, the parasitic capacitance affects the capacitor 500 and produces a voltage error in a measurement voltage which is the voltage of the capacitor 500 after charged. According to the prior art, a disadvantage arises in that among such parasitic capacitances, a ground capacitance Cs may generate a voltage error. This voltage error .DELTA.V is given in the following expression (B). .DELTA.V=.SIGMA.Cs/C.times.V(n-1) (B) [0008] Herein, reference character Cs denotes a ground capacitance, and .SIGMA.Cs designates the sum total of (N+1) ground capacitances in all which are connected to the upper electrode of the capacitor 500. According to the prior art, the sampling switch 400 operates so that the capacitor 500 is charged by the chosen battery cell. After the sampling switch 400 has been turned off, a lower transfer switch 602 is turned on, so that the capacitor 500's ground potential falls to a grounding voltage. Sequentially, an upper transfer switch 601 is turned on, and thereby, the capacitor 500's voltage is transferred to the A/D converter 700. This helps resolve the disadvantage in that a ground capacitance may cause a voltage error. [0009] However, in the flying capacitor circuit, as the cell-selection switch groups 200, 300 and the sampling switch 400, a photo switch which requires no drive bias is frequently used, such as a photo coupler and a photo MOS FET. In this photo switch, the grounding capacitance is small, specifically, approximately 0.5 pF, but the inter-terminal capacitance is large like 30 to 50 pF. Hence, rather than the grounding capacitance, the inter-terminal capacitance would affect the voltage error. Specifically, when the cell-selection switch groups 200, 300 and the sampling switch 400 have been turned on, the electric charge stored by the inter-terminal capacitance while being turned off moves to the capacitor 500. Thereby, a voltage error takes place in the capacitor 500. [0010] Furthermore, as the capacitor 500, if a capacitor which has a capacitance of about 0.2 .mu.F is used, the voltage error caused by the ground capacitance can be narrowed to such a degree that no problem could practically be raised. [0011] Moreover, when the cell-selection switch groups 200, 300 which choose a battery cell targeted for measurement have been turned on, the transfer switch 600 is kept turned off. Hence, this switch's inter-terminal capacitance prompts the turned-on cell-selection switch groups 200, 300 to connect the battery-cell group 100 and the A/D converter 700 so that an electric current alternates. When an electric current passes between the battery cell targeted for measurement and the capacitor 500, an over-voltage caused by this battery cell's voltage is applied to the A/D converter 700. In some cases, the A/D converter 700 may be destroyed. SUMMARY OF THE INVENTION [0012] It is an object of the present invention to provide a voltage measurement apparatus and an electrically-driven tool which are capable of narrowing the voltage error caused by the inter-terminal capacitance of an electric switch and measuring the voltage of a battery cell more precisely. In addition, it is another object of the present invention to provide a voltage measurement apparatus and an electrically-driven tool which are capable of preventing an over-voltage from being applied to a measurement section such as an A/D converter when an electric current passes between a battery cell targeted for measurement and a capacitor. [0013] A voltage measurement apparatus according to an aspect of the present invention which measures the voltage of a battery-cell group that is made up of a plurality of battery cells connected in series, comprising: a capacitor; a sampling switch which is formed by an electric switch, among the battery cells which make up the battery-cell group, electrically connects any one or more battery cells targeted for measurement to the capacitor so that the capacitor is charged by these battery cells targeted for measurement, and electrically separates the battery cells targeted for measurement from the capacitor after the capacitor is charged; a measurement section which measures the voltage of the capacitor after the sampling switch electrically separates the capacitor and the battery cells targeted for measurement, and acquires this voltage as a measurement voltage of the battery cells targeted for measurement; a transfer switch which is formed by an electric switch, and electrically connects the capacitor and an input terminal of the measurement section after the sampling switch electrically separates the battery cells targeted for measurement and the capacitor; and an over-voltage prevention switch which is formed by an electric switch, and grounds the input terminal of the measurement section by turning on immediately before the sampling switch electrically connects the battery cells targeted for measurement and the capacitor. [0014] A voltage measurement apparatus according to another aspect of the present invention which measures the voltage of a battery-cell group that is made up of a plurality of battery cells connected in series, comprising: a capacitor; a sampling switch which is formed by an electric switch, among the battery cells which make up the battery-cell group, electrically connects any one or more battery cells targeted for measurement to the capacitor so that the capacitor is charged by these battery cells targeted for measurement, and electrically separates the battery cells targeted for measurement from the capacitor after the capacitor is charged; a measurement section which measures the voltage of the capacitor after the sampling switch electrically separates the capacitor and the battery cells targeted for measurement, and acquires this voltage as a measurement voltage of the battery cells targeted for measurement; and a transfer switch which is formed by an electric switch, and electrically connects the capacitor and an input terminal of the measurement section after the sampling switch electrically separates the battery cells targeted for measurement and the capacitor, wherein the measurement section: calculates a calculation measurement voltage which is the voltage of the capacitor charged by the battery cells targeted for measurement, using an equivalent circuit which indicates the inter-terminal capacitance of the sampling switch; calculates the ratio of this calculation measurement voltage to the measurement voltage; multiplies the measurement voltage by this ratio; and thereby, corrects the voltage error of the measurement voltage. [0015] An electrically-driven tool according to another aspect of the present invention, comprising: a battery-cell group which is made up of a plurality of battery cells connected in series; a motor which is driven by electric power from the battery-cell group; an inverter section which converts DC electric power outputted from the battery-cell group into AC electric power and supplies the AC electric power to the motor; and the voltage measurement apparatus according to claim 1. [0016] An electrically-driven tool according to another aspect of the present invention, comprising: a battery-cell group which is made up of a plurality of battery cells connected in series; a motor which is driven by electric power from the battery-cell group; an inverter section which converts DC electric power outputted from the battery-cell group into AC electric power and supplies the AC electric power to the motor; and the voltage measurement apparatus according to claim 8. BRIEF DESCRIPTION OF THE DRAWINGS [0017] FIG. 1 is a circuit diagram, showing the configuration of a voltage measurement apparatus according to an embodiment of the present invention. [0018] FIG. 2A is a circuit diagram, showing the configuration of a photo coupler which is an example of the sampling switch. [0019] FIG. 2B is a circuit diagram, showing the configuration of a photo MOS FET which is an example of the sampling switch. [0020] FIG. 3 is a timing chart, showing an operation of this voltage measurement apparatus. [0021] FIG. 4 is a timing chart, showing the effect of a diode over over-voltage protection without an over-voltage prevention switch. Continue reading about Voltage measurement apparatus and electrically-driven tool... Full patent description for Voltage measurement apparatus and electrically-driven tool Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Voltage measurement apparatus and electrically-driven tool patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Voltage measurement apparatus and electrically-driven tool or other areas of interest. ### Previous Patent Application: Minimum battery voltage detection and measurement Next Patent Application: Energy saving system and method Industry Class: Electricity: battery or capacitor charging or discharging ### FreshPatents.com Support Thank you for viewing the Voltage measurement apparatus and electrically-driven tool patent info. 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